This invention relates to medical equipment used in the fields of anesthesiology and emergency airway management. More particularly, the invention relates to an endotracheal tube used in conjunction with a fiberoptic bronchoscope, or other stylet, to overcome intubation difficulties.
Provision of anesthesia to patients during surgical procedures requires ensuring adequate respiratory function. This is most often accomplished by use of an endotracheal tube (ETT). Placement of an endotracheal tube for support of respiration is a critical step in the provision of anesthetic patient care. Placement of the ETT is performed most often under direct visualization using a laryngoscope. However, this procedure can be difficult to accomplish due to anatomic anomalies. Often, a fiberoptic bronchoscope (FOB), or other intubating stylet, is used to overcome these instances of difficult intubations. Use of an FOB allows visualization of the upper airway structures and visual confirmation that the trachea has been entered. Once the trachea has been entered, the FOB is used as a stylet guide to place an ETT. The ETT is slid over the FOB into the trachea. Once the ETT has been successfully placed in the trachea, the FOB is withdrawn and the patient can be ventilated. Other types of stylets are also known.
The currently utilized ETTs were originally designed for intubation under direct visualization and without consideration of use in conjunction with an FOB or other intubating stylet. Their design incorporates a constant diameter tube with a leading edge. When using a standard ETT over an FOB, or other intubating stylet, the leading edge can become impacted on the laryngeal structures causing trauma, delay, or failed intubation.
Endotracheal tubes are in general flexible breathing conduits constructed of medical grade plastics that are adapted to be placed in the patient's trachea. The proximate end of the ETT has a standard fitting allowing connection to a source of pressurized gas such as oxygen and anesthetic gases. The distal end is open to deliver these gases to the trachea and lungs of the patient. The distal end usually has a side hole to aid in equal ventilation of both lungs should the ETT be inaccurately positioned. This side hole is not intended to, nor does it, decrease ventilatory resistance in an ETT that is correctly positioned. The ETT typically has an inflatable bladder or balloon which can be inflated once the ETT is in place within the trachea. This seals the trachea allowing positive pressure ventilation to the lungs and protecting them from secretions and gastric contents. During the intubation process the ETT traverses the mouth, pharynx, larynx, and trachea of the patient and is ultimately placed in the correct position within the trachea without causing damage to bodily structures. Various devices are available to assist with this process, the most important of them being the fiberoptic bronchoscope.
An FOB consists of three basic parts, a proximal control assembly which includes an eyepiece for viewing, an elongated shaft housing fiberoptic bundles, channels, and control wires, and a distal tip containing optics . In use, a high intensity light source is connected via the proximal control assembly for transmission through the fiberoptic bundles. The fiberoptic bundles transmit the light to the distal tip where it is used to illuminate the object to be viewed. Optics located in the distal tip transmit the image through another fiberoptic bundle to the proximal control assembly where the image can be viewed with ones eye or transmitted to a TV monitor for viewing.
In certain situations an FOB is used in conjunction with an ETT to intubate a difficult airway. This is sometimes anticipated prior to anesthetizing a patient but more often is an emergency procedure in a patient who is discovered to have a difficult airway after being anesthetized. In either situation, an appropriate size ETT for the patient is chosen and threaded onto the proximal shaft of the FOB. The tip is of the ETT is lubricated with a water soluble medical lubricant. The procedure for using an FOB as an intubating stylet is the same whether one is using a standard ETT or the described tapered ETT. The upper airways are traversed with the distal tip of the FOB and the laryngeal structures are visualized and identified. The distal tip of the FOB is advanced through the vocal cords and into the trachea. Once entrance of the FOB into the trachea is visually confirmed, the ETT is slid down the shaft of the FOB, using the FOB as an intubating stylet. The tip of the ETT must traverse the larynx prior to entering the trachea, and it is at this point resistance and obstruction to advancement is not infrequently encountered. Thereafter the ETT must be positioned accurately within the trachea and is done so either by direct visualization of the bronchi and carina (the first division of the trachea) through the FOB, or by using predetermined norms for ETT position and listening to breath sounds. Once positioned and the tracheal balloon inflated, the FOB is removed from the ETT. The proximal end of the ETT is then connected to a pressurized gas source and the patient is ventilated.
Trauma from ETT placement may cause bleeding, swelling, laryngospasm, patient discomfort and hoarseness. Delayed or failed intubation can cause brain damage and/or death. This cause of delayed, traumatic, or failed intubation when using an FOB/ETT combination is not infrequent and is documented in the anesthesia literature. For example, Ovassapian states: "In 20-30% of patients, even though the fiberscope has entered the trachea, the endotracheal tube impinges on the larynx and cannot be advanced into the trachea. It is postulated that the tube catches on the epiglottis or on the vocal cords or that it lodges in the pyriform sinus."
Benumof states: "The free lumen of the endotracheal tube predisposes the tube to move away from the the insertion cord of the FOB and catch the laryngeal structures, therefore interfering with the smooth entrance of the tube into the trachea." Brull et al report that fully 13 of 20 FOB assisted intubations using a standard ETT were unsuccessful on the first attempt. Moreover, 7 of 20 patients were unable to be intubated using this technique (standard ETT over an FOB) on the third attempt. They state: "Furthermore, repeated attempts at passage may result in airway bleeding, damage to the arytenoid cartilages or epiglottis, or swelling of the airway, making subsequent endotracheal intubations attempts more difficult." Failed intubation is a significant cause of anesthetic related brain damage, death, and malpractice litigation.
The same problem has been described when using standard ETT's over other intubation stylets. The problem is most severe in the instance of retrograde intubation. Retrograde intubation involves placing a guide wire through the crico-thyroid membrane and bringing it out through the patient's mouth. The wire is then used as a stylet guide for an ETT. Because of the relatively large discrepancy between the thin wire (0.038-inch outer diameter) and the ETT (7-8 millimeters internal diameter), the tip of the ETT often impinges upon the larynx.
Several ETTs and other devices have been designed for specific functions and to overcome specific difficulties related to the difficult airway. For example, Ring, Adair, and Elwyn, in U.S. Pat. No. 3,964,488, seek to overcome the problems of ETT kinking and obstruction by incorporating a preformed angle in the shaft of an ETT. Carden, in U.S. Pat. No. 4,041,936, describes an ETT designed for use during fiberoptic bronchoscopy of the lungs which simplifies the procedure. Vilasi, in U.S. Pat. No. 3,968,800 describes a "Device For Insertion Into A Body opening." One embodiment is an endotracheal tube with an adjustable external circumference which seeks to overcome the need to stock multiple size ETTs and to supplant the need for a tracheal balloon. Adair, in U.S. Pat. No. 5,329,940 describes an "Endotracheal Tube Intubation Assist Device" which couples an FOB with a television monitor to assist with the problem of difficult intubation. Cook Medical markets a retrograde intubation kit, which also seeks to address the problem of the difficult airway.
Vilasi describes a device which generally suffers from complexity, and is therefore more expensive to manufacture, is more user dependent in its correct operation and application than a simpler device, and is more time consuming to operate than a simpler device designed for the same purpose. Using this device as an ETT would raise safety issues as well. One can see that an FOB placed through this device in the non-expanded configuration would significantly interfere with ventilation. This is a serious drawback of the design for use with an FOB, as the ability to visualize anatomic structures while maintaining sufficient ventilation is often necessary or desirable, such as when one is checking for corret placement of the ETT within the trachea. This is accomplished by using an FOB bronchoscopy adaptor which allows the FOB and pressurized gases to be delivered through the ETT at the same time. Attempting to intubate a patient or position the device by moving it in the expanded configuration (intentionally or unintentionally), within the trachea, would risk laceration of the trachea or other upper airway structures, a potentially disastrous complication. Using the device of Vilasi in solelynhe closed configuration would be limited by the increase in resistance to gas flow caused by narrowing the distal end according to Poiseuille's law which states resistance is inversely proportional to the inside radius of the conduit to the 4th power. Hence, small decreases in ETT size give large increases in airway resistance. Therefore, the more useful the device of Vilasi is for intubating difficult airways over a stylet, the less useful the device becomes as a breathing conduit due to the increase in airway resistance.
Adair utilizes a standard ETT in conjunction with his device for assisted intubations. The standard ETT depicted in Adair is not tapered, has a leading edge, and an opening at the distal end which aids in the equal dispersion of oxygen into the lungs. Its use with a standard ETT is therefore subject to the same problems described above, stemming from size discrepancy and the leading edge.
Others in the art teach using a standard ETT for instances when an intubating stylet of one type or another are used. Examples of intubating stylets include FOB's, tracheal tube changers, tracheal tube introducers and guides, and wires used in retrograde intubation kits. For example, the ETT illustrated in the retrograde intubation and tracheal tube changer literature is of standard design. Olympus, the leading FOB manufacturer, depicts a standard ETT in their literature.
The problem of the tube tip catching on the laryngeal structures is in part a function of the discrepancy between the diameter of the intubating stylet and the ETT, causing the leading edge to be oriented incorrectly as the distal tip approaches the larynx. Attempts to overcome this problem have been made. For example, Cook Medical includes an obturator sheath which functions as a spacer in its retrograde intubation kit. The spacer is fitted over the wire after a retrograde intubation wire has been placed, after which the ETT is slid down the combined wire/spacer assembly. This adds another step and time to a procedure in which time is of the essence but is deemed necessary to address the size discrepancy problem. It also does not necessarily solve the problem, only lessens it by degree. Brull et al. describe having greater success using a spiral wound, more flexible ETT than a standard ETT for fiberoptic assisted intubations. They postulate that improved performance was due to the increased flexibility of the ETT, and to a less acute angle of the leading edge relative to the longitudinal axis of the ETT as opposed to the standard ETT. They also note that the Spiral Wound ETT was 10-20 times the cost of a standard ETT and that 5% of the time intubation using the spiral wound ETT and an FOB was unsuccessful in their series. The described ETT of the present invention represents an improvement over the prior art for this purpose.